The ADS816x has two separate power supplies: AVDD and DVDD. The internal reference, reference buffer, multiplexer, and the internal LDO operate on AVDD. The ADC core operates on the LDO output (available on the DECAP pin). DVDD is used for setting the logic levels on the digital interface. AVDD and DVDD can be independently set to any value within their permissible ranges. During normal operation, if any voltage on the AVDD supply drops below the AVDD minimum specification, then the AVDD supply is recommended to be ramped down to ≤ 0.7 V before power-up. Also during power-up, AVDD must monotonously rise to the desired operating voltage above the minimum AVDD specification.
When using an internal reference, set AVDD so that 4.5 V ≤ AVDD ≤ 5.5 V.
The AVDD supply voltage value defines the permissible range for the external reference voltage, VREF, on the REFIO pin. To use the external reference voltage (VREF), set AVDD such that 3 V ≤ AVDD ≤ (AVDD + 0.3) V.
As shown in Figure 106, place a minimum 1-µF decoupling capacitor between the AVDD and GND pins and between the DVDD and GND pins. Use a minimum 1-µF decoupling capacitor between the DECAP and GND pins.
There are no specific requirements with regard to the power-supply sequencing of the device. However, issue a reset after the supplies are powered and stable to ensure the device is properly configured.